A typical force measurement device, also known as load cell, consists of a load sensing element which deforms elastically in proportion to applied load. This in turn changes the electrical properties of sensitive elements such as strain gauges bonded to the load sensing element. Such a change in electrical properties can be correlated to the applied load. Force transducers, in industrial applications, typically use this principle.
The sensitivity of a force measurement device is defined as the ratio of the change that can be measured in the physical parameter to the smallest change in the force actually applied. The higher the sensitivity, the better the resolution of the force measurement device is. The sensitivity of the force measurement device is improved either by mechanical amplification of elastic deformation or electrical amplification of the electrical property like voltage or current.
Force measurement devices are typically of two types: (a) proving ring based, and (b) strain-gauge based. In the proving ring based load cells, the linear elastic deformation, along the loading axis of the ring shaped force sensing element, is measured directly (without any mechanical amplification) to indicate the applied force. The sensitivity of the force measurement device is limited by the sensitivity of the displacement sensor, typically linear variable differential transformer (LVDT), used to measure the elastic deformation. In the strain-gauge based force measurement devices, a set of calibrated foil resistance strain-gauges are mounted in a particular pattern on flexural arms to pick up compressive or tensile strain. These strain-gauges are arranged to form an electrical circuit called full Wheatstone's bridge, the output voltage of which is correlated to the force applied to the load sensing element. In these prior art load cells neither the elastic deformation nor the electrical property is amplified but the output electrical signal, which is typically in the order of mV (millivolts), is amplified to V (volts) via additional electronic signal conditioning boards. However, the amplification of the electrical signal results in high noise-to-signal ratio. The better reported resolution of these load cells is in the order of 0.02-0.05% of the full scale. Such amplification of electrical signal involves use of analog electronics, such as analog-to-digital converter, signal conditioning hardware, etc.